THz輻射光導天線陣列之研製與特性

Abstract

本論文主要在探討光導天線陣列元件的特性。由於，單一天線很容易在光太強的情況之下就飽和，因此本論文製做天線陣列克服此問題。我們已經成功的製做陣列式的光導天線，利用我們設計出來的光導天線陣列，以光導天線陣列上各單一天線輻射出的THz互相干涉，來增強遠場的THz輻射，進而達到在不讓元件飽和的情況下，能輻射出更強的THz。我們模擬推導了天線陣列的遠場結果，用程式的計算和我們量測的結果做比較，明顯得到加強訊號的效果。另外，我們比較了單一天線和設計出來的天線陣列的量測結果，說明天線陣列的訊號強度比單一天線的訊號強度更為加強。 以半絕緣性砷化鎵和砷離子佈值砷化鎵（50,100,200 KeV）做為基板，其中砷離子佈值的濃度為5E15，佈植完後，經過三十分鐘600□C的退火製程。利用適合小線寬的正光阻AZ6112以光阻厚度約12000Å，搭配鍍上Ni:Ge:Au合金（300 Å:700 Å:1000Å），成功的製做出天線陣列。 利用光脈衝約130fs、波長為800nm的被動鎖模（使用飽和吸收體）鈦藍寶石雷射做為光源，使用光導天線，搭配鎖相放大器和步進馬達來做量測。運用自行架設的光纖，將雷射光導進天線陣列。從時域上的分析，我們可以看出當雷射光照射在三個gap上時，量測到的THz訊號，相當於是我們分別將雷射光照射在三個gap上，所量測到的THz訊號之間的干涉，此結果與理論相符合。在比較單一天線和天線陣列的訊號，我們得到天線陣列訊號強度約為單一天線訊號的2.18倍(SI-GaAs)，此結果也與理論算出來的3倍相近。

We have studied the characteristics of photoconductive antenna array. Because the photoconductive antenna is easily saturated when the power of pumping light is higher, we fabricate photoconductive antenna array to solve this problem. We have fabricated photoconductive antenna array successfully. By the interference of the THz radiation of each antenna of our designed photoconductive antenna array, we enhance the THz radiation in the far field. And we can get higher amplitude of electric field of THz radiation when the antenna is unsaturated. We proved and simulated the far field of the THz radiation of photoconductive antenna array. By comparing the calculation of program with the measured result by us, we can get enhanced effect on THz signal obviously. Besides we compare the measured result of single antenna with that of our designed photoconductive antenna array. We use SI-GaAs and GaAs:As+ (50, 100, 200 KeV) for the substrate. The dosage of the implanted As+ of GaAs:As+ is 5E15, and after implanting, we anneal the substrate in 600□C for 30 mins. By using positive photo-resistance (AZ6112) suiting small line-width (the thick of positive photo-resistance is 12000 Å), and plating metals (Ni:Ge:Au = 300Å:700 Å:1000Å), we fabricated photoconductive antenna array successfully. By using a passive-mode-locked(SBR) Ti Sapphire Laser (λ=800nm) generating 130fs optical pulses, we use photoconductive antenna with lock-in amplifier and actuator to measure THz. And we use the fiber set up by our-self to guide the light into photoconductive antenna array. To analyze the THz radiation in time domain by comparing the signal of single gap with that of multi gap, we can see that the signal of multi gap is the interference of the signal of each single gap. This measured result matches the result of the theory. By comparing the signal of single antenna and antenna array, we find that the signal of antenna array is 2.18 times the signal of single antenna (SI-GaAs). This result is similar to the calculated result by the theory (3times).